- South
Korean scientists have developed a new high-performance lithium ion battery
which is stable at high temperatures

July 3, 2015

Lithium ion batteries (LIBs) are a
huge technological advancement from lead acid batteries which have existed
since the late 1850’s.Thanks to their
low weight, high energy density and slower loss of charge when not in use, LIBs
have become the preferred choice for consumer electronics.Lithium-ion cells with cobalt cathodes hold
twice the energy of a nickel-based battery and four-times that of lead
acid.Despite being a superior consumer
battery, LIBs still have some drawbacks.Current manufacturing technology is reaching the theoretical energy
density limit for LIBs and overheating leading to thermal runaway i.e. “venting
with flame” is a serious concern.

South
Korean researchers at the Center for Self-assembly and Complexity, Institute for
Basic Science (IBS), Department of Chemistry and Division of Advanced Materials
Science at Pohang University, have created a new LIB made from a porous solid
which greatly improves its performance as well as reducing the risks due to
overheating.

Since
2002 there have been over 40 recalls in the US alone due to fire or explosion
risk from LIBs used in consumer electronic devices.These types of batteries, in all of their
different lithium-anode combinations, continue to be an essential part of
modern consumer electronics despite their poor track record at high
temperatures.

The
Korean team tried a totally new approach in making the batteries.According to Dr. Kimoon Kim at IBS, “we have already investigated high and highly
anisotropic [directionally dependent] proton conducting behaviors in porous
CB[6] for fuel cell electrolytes. It is possible for this lithium ion
conduction following porous CB[6] to be safer than existing solid lithium
electrolyte -based organic-molecular porous-materials utilizing the simple
soaking method.” Current LIB technology relies on intercalated lithium which
functions well, but due to ever increasing demands from electronic devices to
be lighter and more powerful, investigation of novel electrolytes is necessary
in order.

The
new battery is built from pumpkin-shaped molecules called cucurbit[6]uril
(CB[6]) which are organized in a honeycomb-like structure.The molecules have an incredibly thin 1D-channel,
only averaging 7.5 Å [a single lithium ion is 0.76 Å, or .76 x 10-10 m]
that runs through them.The physical
structure of the porous CB[6] enables the lithium ions to battery to diffuse
more freely than in conventional LIBs and exist without the separators found in
other batteries.

In
tests, the porous CB[6] solid electrolytes showed impressive lithium ion
conductivity.To compare this to
existing battery electrolytes, the team used a measurement of the lithium
transference number (tLi+) which was recorded at
0.7-0.8 compared to 0.2-0.5 of existing electrolytes.They also subjected the batteries to extreme
temperatures of up to 373 K (99.85° C), well above the 80° C typical upper temperature
window for exiting LIBs.In the tests,
the batteries were cycled at temperatures between 298 K and 373 K ( 24.85° C and 99.85° C) for a
duration of four days and after each cycle the results showed no thermal
runaway and hardly any change in conductivity.

Various
conventional liquid electrolytes can incorporate in a porous CB[6] framework
and converted to safer solid lithium electrolytes. Additionally, electrolyte usage is not limited
to use only in LIBs, but a lithium air battery potentially feasible. What makes this new technique most exciting is
that it is a new method of preparing a solid lithium electrolyte which starts as
a liquid but no post-synthetic modification or chemical treatment is needed.

-About
the Institute for Basic Science (IBS)
IBS was founded in 2011 by the government of the Republic of Korea with the
sole purpose of driving forward the development of basic science in Korea It
comprises a total of 50 research centers in all fields of basic science,
including mathematics, physics, chemistry, life science, earth science and
interdisciplinary science.
IBS has launched 24 research centers as of
January 2015.There are eight physics, one mathematics, six chemistry, seven
life science, and two interdisciplinary research centers.